Thursday, 25 October 2012

Although individuals of a particular species frequently differ in a variety of characteristics, the implications of those differences are often not well understood. One exception to this general rule is the known positive impacts of size and condition, but what about the effects of certain preferences and choices--the tendency, for example, to utilize one type of habitat rather than another? A recent study on woodland caribou (Rangifer tarandus caribou) suggests that individual variations can literally be a matter of life and death--in this case not for the animals themselves, but for their offspring.

The study, performed north of Quebec City by a quintet of Canadian researchers, examined the habitat preferences of 23 adult female caribou over a 2-year study period. The researchers were interested in determining whether caribou mothers' habitat selection could affect their reproductive success by exposing calves to potential predators. The habitat in question--located within Quebec's Charlevoix region--varied widely, containing areas that were relatively undisturbed, some that had recently been logged ("cutovers"), and others that had previously been logged but where the vegetation had just begun to grow back in ("non-regenerated areas").

All females were fitted with GPS collars, allowing the scientists to determine where the caribou were located--and, therefore, what type of habitat they were utilizing. Monitoring efforts were particularly intense during the spring calving period, since the researchers wished to capture calves and fit them with radio collars. While the habitat usage patterns of calves could be determined from their mothers' GPS signals, the radio collars were important for allowing researchers to monitor survivorship of juvenile caribou and, when the calves died, to locate their remains. In cases of calf mortality, the researchers examined both carcasses and the surrounding habitat in order to determine the cause of death.

Pregnant females all gravitated towards habitats located on upper slopes--areas where grey wolves (Canis lupus) were less likely to be found. The usefulness of this preference was revealed by the juvenile mortality data, which showed that only 1 of 22 predated calves died from a confirmed wolf attack. However, females that showed particularly high preference for these areas--in other words, those who utilized only this habitat rather than wandering up and down the slopes--were much more likely to lose their calves to predation. This is because the high-elevation areas were also frequented by black bears (Ursus americanus), which appeared to be responsible for the other 21 predation events (only 2 calves died of natural causes, bringing the entire death toll to 24).

(A black bear, one of the caribou's two main predators. Image courtesy of Wikipedia.)

The impacts of the anthropogenically modified habitat types were interesting. Calf mortality was not strongly related to active selection of cutovers, suggesting that logging--or, at least, use of recently logged areas--may not be particularly detrimental to caribou fitness. One potential reason for this is that cutovers have not yet been repopulated by moose, the presence of which brings an influx of wolves; at the same time, there is not yet enough food here to support foraging black bears. Not only are these sites relatively empty of predators, but they also provide good cover near the ground, giving young caribou a place to hide should they need it.

Calves were, however,more likely to be predated when their mothers did not avoid non-regenerated areas. This probably stems from the fact that these patches offered more sustenance to black bears, and were therefore more likely to contain caribou predators. There was also an interesting interaction between vegetation and the presence/absence of roads, such that calf loss was more common in areas with both high road density and few (or no) mature tree stands. Again, this is probably related to the fact that these habitats support more potential predators, as well as the fact that these same predators often use roads in order to move through the habitat more easily.

(Regenerating forest at a former logging site. Image courtesy of the NW Council.)

These findings suggest not only that individual variations in habitat selection affect reproductive success, but also that caribou may actually benefit from anthropogenic activities: The ungulates appear to be safest in the most human-disturbed areas, though the researchers suggest their results should be treated with caution because the sample size was relatively low. The study also highlights the interconnectedness of organisms at different "trophic levels," or positions within the food web. Variations in the abundance of vegetation impact moose, caribou, and black bears, while differences in moose and caribou populations affect both black bears and wolves. All of these organisms can, in turn, be affected by anthropogenic activities such as logging and the creation of roads. Thus, this work is an important reminder that the effects of humans can often be subtle, complex, and indirect.

Sunday, 7 October 2012

Every year, anywhere from 100 million to 1 billion American birds are thought to die after colliding with windows. Planners and builders have tried a variety of techniques to reduce collisions, but, according to a trio of researchers from the University of Alberta, these mitigation efforts are ultimately stymied by a poor understanding of what environmental conditions encourage collisions in the first place.

The Canadian team recently looked into this issue with the help of conservation biology undergraduate students who assisted with the study as part of their coursework. The main goal of the research was to identify the habitat characteristics associated with collisions; in particular, the research team investigated whether birds were more likely to be injured in urban versus rural environments, at houses versus apartments, near places with versus without bird feeders, and on older or younger properties (which potentially vary in the extent of surrounding vegetation). In addition to these environmental data, the research team also collected information on the number of birds hurt, the species of birds involved in collisions, and whether collision rates varied between seasons.

(The authors explored whether the presence of bird feeders, among other environmental factors, increased the likelihood of collisions with windows.)

The undergraduate students were responsible for drafting volunteers to provide all of these data. To this end, they created public-awareness pamphlets that were distributed to friends, family, and colleagues, both in paper form and via online social media. The pamphlets asked would-be participants to visit the conservation course website in order to read more about the project and enter information about avian collisions at their homes. The questionnaire covered eight "core" questions that collected information on participant demographics, observation and timing of bird collisions, length of home occupation, type of residence, presence of bird feeder, and location of home. This latter detail was provided in the form of a postal code, which was used to link the survey responses to census data (on neighborhood age) and to locate the home on Google Earth so that it could be classified as either urban or rural. The surveys also asked residents to identify which species were involved in collisions.

Of the ~1,800 people who participated in the survey over the two-year study period, approximately half remembered a bird-window collision at some point in the past; just over a third of individuals indicated that a collision had occurred within the past year alone. Although the mean collision rate was only 1.7 birds per year, this varied widely from one home to the next; several dozen collisions were reported at some residences, and the worst tally was 84 at a single home in a single year. Luckily, (known) mortality rates averaged less than 1 bird per year.

(Installation of decals may be one way to reduce the number of bird-window collisions. Image courtesy of Whispering Pines.)

Generally speaking, rural residences had more collisions and mortalities than urban residences; bird-window encounters were least common at apartments. Feeders tended to be associated with a higher number of collisions and mortalities, though dynamics varied a bit in urban and rural environments. There was some evidence that age of neighborhood influenced the likelihood of collision, but only in urban areas. Both the number of collisions and the number of deaths peaked in the summer and were lowest in the winter--perhaps because avian abundances vary greatly between these two seasons, since a large proportion of Canadian birds head south for the winter. Sparrows were the most common casualty of collisions, with chickadees and robins close behind; for all three species, a higher percentage of birds survived than died, though the difference was pretty slim for robins.

One of the reasons the authors were interested in pursuing this research was that there is a relative dearth of descriptive work on avian-window collisions. Results of the few studies that have been conducted have been used to create what the authors call a "social construction," or a widespread belief about something (in this case, the danger of windows) that is not actually based on scientific fact. Thus, the current study was developed not only to ascertain just how many birds truly are impacted by windows each year, but also to examine the environmental correlates of collisions--information that could be vital for developing useful conservation and management plans. Given the contributions of undergraduate students and members of the public, an additional benefit of the study is that it contributes to education and awareness.

(American robin, Turdus migratorius, a species that was particularly susceptible to both collisions, in general, and collision mortality. Image courtesy of Wikipedia.)

The researchers acknowledge some flaws in their work--in particular, the inaccuracies and biases associated with self-reporting--but they still feel that their results have made some useful contributions to the field. For example, their finding that feeders are associated with a higher likelihood of collision suggests that people should be careful to place seed and suet dispensers away from windows, or make their windows more obvious (e.g., by decorating them with decals and trimming back vegetation). By identifying that rural and older homes are more likely to experience collisions, the study helps show managers and planners which regions to focus on when attempting to mitigate the negative effects of windows.

Despite these important findings, more work is needed for the future. Birds that appear to survive collisions may simply fly off and die elsewhere. This makes it difficult to accurately measure the effects of windows on individual health and fitness. Thus, better demographic data are needed, as are, potentially, tracking studies that follow injured birds after they fly off. This information will also be important for understanding the long-term (population-level) impacts of collisions; it may be that the benefits of supplemental feeding outweigh the drawbacks of increased exposure to windows, but it might also be the case that birds would be better off without either the bird seed or the windows. The authors recommend that future studies move away from opportunistic observations (as made in the current project), and instead involve either experimentation or a "snapshot" approach, during which researchers would undergo an intensive period of comprehensive data collection. Given their positive experiences with mobilizing the troops via the Internet, they recommend the use of online social network sites for increasing participation in any future work on avian collisions.

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Tuesday, 2 October 2012

Neanderthals get a lot of flack for being more "primitive" and less "advanced" than we humans, but there is an increasing evidence that they may not have been that different from our early ancestors. For example, researchers are now pretty certain that Neanderthals interbred with modern humanswho shared their European habitats. While this suggests a greater degree of physical similarity than we once realized, there also appear to be cognitive overlaps between the two species as well. Recently, for instance, an international team of researchers published a paper in PLoS ONE reporting that Neanderthals, like early modern humans, harvested bird feathers for decorative purposes.

(Red-billed choughs, Pyrrhocorax pyrrhocorax, were one of several cliff-loving species found at Paleolithic sites. Image courtesy of Wikipedia.)

This finding is exciting for two main reasons. First, to quote the authors directly, "regular and systematic exploitation of flying birds for food is considered to be a hallmark of behavioural modernity, exclusive to anatomically modern Homo sapiens after 50 thousand years ago." Although there have been a few previous findings indicating that birds were an occasional prey item of Neanderthals, researchers have typically argued that use of avian species was "opportunistic and unsystematic." Thus, any evidence that Neanderthals repeatedly collected birds (regardless of how the animals were eventually used) indicates that we humans were not the only hominins capable of recognizing the potential of these particular sources of material--not to mention figuring out how to go about getting them.

The second point of interest pertains to the use of birds not for meat--or, at least, not just for meat--but for feathers and claws. Given how these bits were utilized by early humans, as well as by human descendants in nearly every known culture around the world, it is likely that the Neanderthals were collecting these features for personal ornaments or some other decorative purpose. This sort of behavior has generally been considered beyond the capacity of Neanderthals, and so the new evidence is suggestive of "unprecedented cognitive abilities."

(Cut-marks from early stone tools were found on many bird bones at three sites in Gibraltar--Gorham's, Vanguard, and Ibex Caves. Image courtesy of PLoS ONE.)

Aware that this possibility might be met with skepticism, the authors were sure to perform as comprehensive a study as possible. They first compiled a database of 1,699 archaeological and paleontological sites in which avian fossils had been identified. They were particularly interested in raptors and corvids because these two groups of birds are often seen around human settlements and so seemed particularly likely to be accessible to early hunters. An analysis of the database revealed that both Middle Paleolithic sites (those associated with Neanderthals) and Upper Paleolithic sites (those associated with modern humans) contained more raptor and corvid species than paleontological sites. Particularly common were birds that are scavengers, colonial nesters, and/or cliff-dwellers, indicating that hominin hunters were reacting to "a strong ecological signal." Also common--especially in Neanderthal-era sites--were birds with dark wing feathers. If, as this suggests, Neanderthals were specifically targeting species with certain physical characteristics, then these artifacts are evidence of "sophisticated cognitive processes" not previously attributed to these early hominins.

Detailed examinations of 604 "skeletal elements" from 21 species of bird revealed many signs of hominin processing: cut-marks made by Neanderthal stone tools, bones broken just after the birds had died, burns, tooth imprints, and--especially interesting--overextension of the ulnae and humeri. In other words, the wings had been stretched as their feathers were plucked out. The wings had received considerably more attention than other parts of the birds' bodies, and the authors found no evidence that the preponderance of wing bones at their study sites resulted from anything other than especially high levels of hominin interest in these parts of the bird anatomy.

(Map showing the Paleolithic and paleontological sites containing more than 50% of the 18 raptor/corvid species cataloged across the study area. Image courtesy of PLoS ONE.)

Although many of the examined sites were quite distant from each other--2,000 km separate Riparo Fumane and Gibraltar, for example--the authors could still see a "clear concentration across the western mid-latitude belt." The habitats in these areas are relatively similar, granting Neanderthals and early modern humans consistent access to the same types of bird species. What remains unclear, however, is what sort of forces led hominins in these areas to display similar levels of interest in the wing feathers of raptors and corvids. Did a shared ancestor of both Neanderthals and modern humans pass down this cultural characteristic? Was there behavioral convergence of two groups living in the same region? Is it possible that Neanderthals could have transmitted this trait to modern humans?

Given the current evidence, this may be difficult to determine; for now, the best the authors can do is point out that feather use is a "common characteristic of the two lineages." Further, Neanderthals arrived in Europe several thousand years before modern humans did, and therefore engaged in feather-plucking activities in isolation. Thus, no matter how they learned this behavior and regardless of whatever other mental skills they may have had, these early hominins often maligned for their lack of intellect were clearly capable of "cognitive capacities that included symbolic expression"--a characteristic that the authors feel renders them "distinctly human."

Who is the "Anthrophysist"?

I am a biologist who studies the ways in which anthropogenic disturbance impacts animals (especially birds). I hope that the results of my work, and the work of other researchers like me, can help humans learn how to coexist more peacefully with wildlife. I am also interested in the role that nature has played in shaping human cultures around the world and over the centuries. Although this blog will predominantly focus on scientific research, I hope to occasionally profile some anthropological work as well, in order to better highlight the interconnectedness of humans ("anthro") and nature ("physis").